1. Field of the Invention
This invention relates to a sliding bearing which is multilayered, self-lubricating and maintenance-free, and to a method of making multilayered sliding bearing material. The sliding bearing material according to the invention is comprised of a layer of bronze which is porously sintered onto a metallic supporting body and which has pores which are impregnated with polytetrafluoroethylene (PTFE) by vacuum infiltration.
2. Description of the Related Art
Multilayered sliding bearing materials are widely used in many engineering applications, e.g., machines used in the food and household appliance industries. A high economic efficiency for such machines has been achieved by abandoning complicated lubricating arrangements.
Bearings made from sliding bearing materials are known. Such bearings are comprised of a porous bronze layer sintered onto a steel band and having a sliding layer comprised of PTFE/lead rolled onto the bronze layer in such a way that the sliding layer does not delaminate. Published German Patent Application No. 35 16 649, for example, discloses a self-lubricating bearing. The sliding layer of this bearing is comprised of a mixture of lead oxide and PTFE resin. This sliding layer covers the porous sintered metal layer and fills the pores thereof. This prior art sliding layer projects beyond the sintered the metal layer and has a structure which influences the characteristics of such a bearing. The sliding layer is applied to the sintered metal layer as a paste comprised of PTFE and lead by roller coating.
Published British Patent Application No. 707,065 discloses a vacuum impregnating method for embedding PTFE in the pores of a metallic surface. The surface has a porous layer, but no information is provided with respect to the porosity. Published British Patent Application No. 754,115 discloses a bronze layer having a pore volume of 30%. The pores can be filled by means of any impregnating method. The porosity of the bronze layer is generated by applying a bronze powder having a specific particle size. The porosity formed in this manner is not sufficient for generating a uniform impregnation throughout the entire thickness of the bronze layer, however. At the surface of the bronze layer, the amount of embedded PTFE is greater than in the deeper-lying region.
It is an object of the invention to provide a sliding bearing made of a sliding bearing material which has extremely low friction coefficients and wear rates, and which is also particularly suited for use in the foodstuff industry, particularly for food processing machines.
It is a further object of the invention to provide a sliding bearing material comprising a porous metal layer uniformily impregnated with PTFE so that the PTFE is homogeneously distributed throughout the thickness of the porous metal layer.